1. Field of the Invention
This invention relates to a surface mountable PTC device, more particularly to a surface mountable PTC device suitable for high current applications.
2. Description of the Related Art
FIG. 1 illustrates a conventional surface mountable PTC (Positive Temperature Coefficient) device 1 that is disclosed in U.S. Pat. No. 5,852,397. The PTC device 1 includes a PTC layer 10 of a PTC material, first and second metal foils 11 formed on two opposite surfaces of the PTC layer 10, and first and second terminals 13 extending through the first and second metal foils 11 and the PTC layer 10 so as to contact electrically the first and second metal foils 11. A portion of each of the first and second metal foils 11 is removed by etching so as to divide each of the first and second metal foils 11 into two separate parts and so as to form first and second electrodes 121, 122, which are respectively and electrically connected to the first and second terminals 13, on each surface of the PTC layer 10. The aforesaid PTC device 1 is disadvantageous in that a substantial portion of each metal foil 11 is removed, which results in a significant decrease in the current passing through the PTC device 1. As a consequence, the size of the PTC device 1 is required to be increased for high current applications, which is against the trend toward minimization of the PTC device 1.
FIG. 2 illustrates another conventional PTC device 3 that is prepared by attaching first and second metal foils 31 to two opposite sides of a PTC layer 30, removing an end portion of each metal foil 31 so as to form two recesses in two opposite ends of the PTC device 3 and so as to form first and second electrodes 311, 312 respectively on the sides of the PTC layer 30, forming two insulating layers 32 respectively on the first and second electrodes 311, 312 in such a manner that each insulating layer 32 fills a respective one of the recesses, forming two holes in the ends of the PTC device 3, and forming first and second terminals 351, 352 respectively in the holes in such a manner that the first terminal 351 is electrically connected to the second electrode 312 and that the second terminal 352 is electrically connected to the first electrode 311. The aforesaid PTC device 3 is disadvantageous in that in order to isolate the first electrode 311 from the first terminal 351 and the second electrode 312 from the second terminal 352, an entire end portion of each of the first and second metal foils 31 is removed, which results in a decrease in the areas of the first and second electrodes 311, 312, which, in turn, results in a reduction in the current passing through the PTC device 3.